Ellipsometry is an instrument used for analyzing optical constants, microstructure, and measuring film thickness based on the optical properties of materials. A laser with a known polarization state is directed onto the surface of a thin film. The light undergoes refraction/reflection at the film interface, causing a change in the polarization state of the outgoing light from linear to elliptical polarization. As the alteration in polarization state is associated with the thickness of the film and the refractive index of the material, measuring the change in the polarization state of the outgoing light enables the retrieval of thin film parameters through inverse calculations.

The measurement process of an ellipsometer does not require direct contact with the sample, which prevents surface damage to the material. Furthermore, it does not necessitate a vacuum environment, making it a convenient, rapid, and easily implementable tool for material analysis.

The primary materials analyzed by ellipsometers include semiconductor materials, dielectrics, and polymer materials. Additionally, as ellipsometry measurement is a non-destructive testing technique with minimal impact on the material's surface, it can also be utilized for surface inspection of biological samples.